1. Field of the Invention
The invention relates to an apparatus and a method for manufacturing an electricity storage material.
2. Description of the Related Art
In recent years, lithium ion secondary batteries have been used for hybrid vehicles, electric vehicles, etc. Electrodes of the lithium ion secondary batteries are manufactured by first kneading powder of an active material etc. and a solution of a thickener to produce slurry of an active material (electricity storage material), and then applying the slurry to a base material such as aluminum foil and drying the slurry. This slurry may contain aggregates due to defective dispersion of the powder of the active material etc., metal foreign matter, dust, etc. In this case, a coating jig (slit die) tends to be clogged with the aggregates of the powder of the active material etc. during coating (application) of the slurry. This may cause streaks or crater-like spots in the coating, resulting in defective electrodes.
In order to prevent manufacturing of such defective electrodes, it is necessary to remove the aggregates of the powder of the active material etc. from the slurry of the active material. For example, Japanese Patent Application Publication No. 2013-146644 (JP 2013-146644 A) describes filtration of slurry of an active material with a filter. Japanese Patent Application Publication No. 2012-87039 (JP 2012-87039 A) describes filtration of slurry of an active material with a filtering device. Japanese Patent Application Publication No. 2003-77466 (JP 2003-77466 A) describes filtration of slurry of an active material with addition of alcohol.
In recent years, further improvement in battery performance has been desired. For improved battery performance, the inventors have proposed to perform step-by-step the step of dissolving a thickener, the step of adjusting viscosity of the solution of the thickener, and the step of kneading the solution of the thickener having the adjusted viscosity and powder of an active material etc. However, an undissolved material (microgels) of the thickener may remain as coarse particles in the solution of the thickener. In this case, a coating jig (slit die) tends to be clogged with the microgels as coarse particles of the thickener during coating (application) of slurry. This may cause streaks or crater-like spots in the coating, resulting in defective electrodes.
As described in JP 2013-146644 A, JP 2012-87039 A, and JP 2003-77466 A, a method to prevent manufacturing of such defective electrodes is to remove the microgels as coarse particles of the thickener together with the aggregates of the powder of the active material etc. when filtering the slurry of the active material. However, since the particle size of the microgels as coarse particles of the thickener is typically smaller than that of the aggregates of the powder of the active material etc., the non-aggregated powder of the active material etc. is also removed when the microgels as coarse particles of the thickener are removed. This reduces yield of the slurry of the active material.